A minimally invasive procedure is a medical procedure that is performed through the skin or an anatomical opening. In contrast to an open procedure for the same purpose, a minimally invasive procedure will generally be less traumatic to the patient and result in a reduced recovery period.
However, there are numerous challenges that minimally invasive procedures present. For example, minimally invasive procedures are typically more time-consuming than their open procedure analogues due to the challenges of working within a constrained operative pathway. In addition, without direct visual feedback into the operative location, accurately selecting, sizing, placing, and/or applying minimally invasive surgical instruments and/or treatment materials/devices can be difficult.
For example, for many individuals in our aging world population, undiagnosed and/or untreatable bone strength losses have weakened these individuals' bones to a point that even normal daily activities pose a significant threat of fracture. In one common scenario, when the bones of the spine are sufficiently weakened, the compressive forces in the spine can cause fracture and/or deformation of the vertebral bodies. For sufficiently weakened bone, even normal daily activities like walking down steps or carrying groceries can cause a collapse of one or more spinal bones. A fracture of the vertebral body in this manner is typically referred to as a vertebral compression fracture. Other commonly occurring fractures resulting from weakened bones can include hip, wrist, knee and ankle fractures, to name a few.
Fractures such as vertebral compression fractures often result in episodes of pain that are chronic and intense. Aside from the pain caused by the fracture itself, the involvement of the spinal column can result in pinched and/or damaged nerves, causing paralysis, loss of function, and intense pain which radiates throughout the patient's body. Even where nerves are not affected, however, the intense pain associated with all types of fractures is debilitating, resulting in a great deal of stress, impaired mobility and other long-term consequences. For example, progressive spinal fractures can, over time, cause serious deformation of the spine (“kyphosis”), giving an individual a hunched-back appearance, and can also result in significantly reduced lung capacity and increased mortality.
Because patients with these problems are typically older, and often suffer from various other significant health complications, many of these individuals are unable to tolerate invasive surgery. Therefore, in an effort to more effectively and directly treat vertebral compression fractures, minimally invasive techniques such as vertebroplasty and, subsequently, kyphoplasty, have been developed. Vertebroplasty involves the injection of a flowable reinforcing material, usually polymethylmethacrylate (PMMA—commonly known as bone cement), into a fractured, weakened, or diseased vertebral body. Shortly after injection, the liquid filling material hardens or polymerizes, desirably supporting the vertebral body internally, alleviating pain and preventing further collapse of the injected vertebral body.
Because the liquid bone cement naturally follows the path of least resistance within bone, and because the small-diameter needles used to deliver bone cement in vertebroplasty procedure require either high delivery pressures and/or less viscous bone cements, ensuring that the bone cement remains within the already compromised vertebral body is a significant concern in vertebroplasty procedures. Kyphoplasty addresses this issue by first creating a cavity within the vertebral body (e.g., with an inflatable balloon) and then filling that cavity with bone filler material. The cavity provides a natural containment region that minimizes the risk of bone filler material escape from the vertebral body. An additional benefit of kyphoplasty is that the creation of the cavity can also restore the original height of the vertebral body, further enhancing the benefit of the procedure.
Conventional inflatable bone tamps (IBTs) used in kyphoplasty procedures incorporate balloon catheters that are constructed using two coaxial catheters, with the distal ends of the outer and inner catheters being coupled to the proximal and distal end regions, respectively, of the balloon. Because the inner catheter has a relatively small diameter, during inflation of the balloon, the inner catheter exhibits a degree of longitudinal (i.e., axial) growth, thereby allowing the balloon to grow longitudinally as well.
For many applications, such as use in a kyphoplasty procedure, this longitudinal balloon growth can be beneficial. For example, if the inner catheter is completely inextensible (i.e., cannot extend longitudinally), the balloon inflation will be rather spherical, which in turn can undesirably create local regions of high pressure at the apex(es) of the sphere. On the other hand, if the inner catheter elongation is completely unconstrained, the balloon may not exhibit sufficient radial expansion. Ideally, the limited-elongation expansion profile enabled by a controllably extensible inner catheter can reduce the risk of localized high pressure regions by creating a “flatter”, more oval-shaped inflation profile, while still allowing radial growth sufficient to achieve desired procedure outcomes.
However, because of the variations inherent in catheter manufacturing, it can be difficult to control/predict the extensibility of the inner catheter within a balloon catheter. Historically, this aspect of balloon catheter performance has been of little significance, but the advent of higher pressure applications (such as use in kyphoplasty and other bone environments) has increased the importance of well-defined control over balloon catheter longitudinal growth.
Accordingly, it is desirable to provide surgical tools and techniques that enable controlled longitudinal growth of a balloon catheter during inflation.